Coming from the world of performance cars, I'm often impressed with how most 4WD enthusiasts neglect their tire pressures while on the street. It's fairly common for a 4WD enthusiast to often have all of the necessary equipment in their vehicle, but fail to fully inflate their tires to the proper pressure. There's a definite benefit to running a lower tire pressure once you're off the pavement, but when you're back on it, you need to be sure to properly inflate.
While an under-inflated tire may offer a slightly less harsh ride to the occupants of the vehicle, it's no excuse for not running an appropriate pressure. In addition to having significantly more rolling resistance and negatively impacting your fuel consumption, an under-inflated tire has less sidewall rigidity. That ends up resulting in some undesired handling characteristics, especially if you've installed a roof rack with plenty of kit, or simply a suspension lift that has altered your center of gravity.
It's estimated that if you drive approximately 12,000 miles a year, under-inflated tires can use up to 140 extra gallons of gasoline. That could get you pretty far on a trip, now couldn't it?
Some 4WD owners are very proactive with ensuring that once they leave the trail, they stop and inflate their tires, but when you're in the middle of no where this can be difficult so ensure you're properly equipped—this means a way to re-inflate your tires. We've recently re-published a comprehensive Air Compressor Test that first appeared in Overland Journal a few years back, the article details a few leading air compressors on the market, along with the pros and cons of each.
For some a compressor makes perfect sense, but it's not the only option. Powertank offers a alternative CO2 inflation system that is also capable of running powertools, not just inflating tires.
The little thingy on your wheel that you put air into has a name, it's called a Schrader Valve (often called an American valve as well) it's relatively unknown that a valve cap is an essential component to the Schrader valve. It helps prevent dust and debris from damaging the internal components and causing leaks. The simple solution is to always ensure that you have a valve cap on the unit when you're not inflating or deflating. The problem is that the little caps tend to get lost, they either fly off while driving, or are simply forgotten, often in a pocket. I highly suggest Extreme Outback's No Loss Tire Valve Caps. As you can see above, they have a plastic leash on them to prevent loss, what you can't see is a rubber seal underneath the cap ensuring they hold air and keep debris out. They're available in plastic and aluminum, you can read more about them here.
A proper tire pressure gauge is an essential piece of vehicle kit, while a pencil-type pressure gauge will work, I much prefer a larger standard gauge that offers me the ability to let out air pressure. There's no need to spend a large amount on these, but it's important to use it, and use it often. Generally speaking, front and rear tire pressures should always be nearly identical, and tire pressures on one side of an axle must match the other. If your right front tire is has a higher pressure than your left front tire, the vehicle will push to the side. This can cause uncomfortable driving, and larger issues incase of accident avoidance.
Most modern vehicles will have a page in your owners manual detailing recommended tire pressures, some even have a decal located inside of your door telling you what pressures to run. It's important to note that these pressures were designed around a specific brand and size of tire. While they're usually correct, your tire will have a recommended, and max pressure molded into the sidewall, and if you've changed the brand or size of your tires, it's best to refer to that.
Often times it's the simple things like checking your tire pressures that end up being forgotton. I can't tell you how many times I've gone over my vehicle with a fine tooth comb before a trip, only to forget to check my tire pressures before setting out on a 2,000 mile highway drive. Underinflated tires cost money, upwards of 1-2 MPG...It adds up quick—and I don't think I'll see that money back anytime soon.